With the development of electronic cigarettes, various electronic cigarettes with different structures have been invented. Among these electronic cigarettes, a cotton-free electronic cigarette is a highly popular electronic cigarette right now. The cotton-free electronic cigarette has fewer components than conventional electronic cigarettes, so the assembly of the components of the cotton-free electronic cigarette is easy and the assembled cotton-free electronic cigarette has a simple structure. The cotton-free electronic cigarette uses a liquid percolation piece to directly absorb cigarette liquid, due to temperature difference and/or other reasons, residual vapor easily condenses to form residual liquid, which will be inhaled into a user's mouth if a vapor flow passage of the cotton-free electronic cigarette is arranged in the middle of the cotton-free electronic cigarette to directly reach a mouthpiece. In this aspect, the cotton-free electronic cigarette is inferior to conventional cotton-bearing electronic cigarettes in preventing liquid spill, because cigarette liquid absorption cotton of the conventional cotton-bearing electronic cigarette is able to absorb residual liquid. Thus, how to improve the structure of existing cotton-free electronic cigarette to effectively prevent liquid spill is a problem to be solved.